The present invention relates to a distribution-type compensator and a projection-type liquid crystal display apparatus using the same.
Recently, for a projection display apparatus such as a liquid crystal projector, a demand for downsizing and weight saving has intensified together with a demand for an improved performance. As a method of realizing downsizing and weight saving, there have been proposed a shift method from a three-plate system using three liquid crystal elements to a single-plate system using one liquid crystal element, a method of miniaturizing components with leaving the three-panel system, and the like.
As a method of realizing a downsized optical system for the liquid crystal projector, Patent Literature 1 (Japanese Patent Application Laid-Open Publication No. 2005-2217 61) discloses contents approximately as follows. In an optical system of a liquid crystal projector, a field lens is disposed between a liquid crystal on silicon and a wire-grid type polarization beam splitter hereinafter, called WG-PBS). Blue light, green light, and red light which have been separated from one another by a color separation optical system enter the WG-PBS at an incident angle smaller than 45 degrees. The light having passed through the WG-PBS enters the liquid crystal on silicon via the field lens. The light emitted from the liquid crystal on silicon enters the field lens again and enters the WG-PBS. By disposing the field lens between the reflection-type liquid crystal element and the WG-PBS, a light path of an illumination optical system before light enters the field lens and a light path of an imaging optical system after light has been reflected by the liquid crystal on silicon and passed through the field lens are configured in a non-telecentric manner, which causes a cross dichroic prism and the WG-PBS to be downsized.
In Patent Literature 1, by disposing the field lens between the reflection-type liquid crustal element and the WG-PBS, the light path of the illumination optical system before light enters the field lens and the light path of the imaging optical system after the light has been reflected by the liquid crystal on silicon and passed through the field lens are configured in the non-telecentric manner, which causes the cross dichroic prism and the WG-PBS to be downsized. Here, a telecentric optical system is an optical system in which an optical axis and a principal light ray are assumed to be parallel on one side of a lens.
As disclosed in Patent Literature 2 (Japanese Patent Application Laid-Open Publication No. 2007-101764) and Patent Literature 3 (Japanese Patent Application Laid-Open Publication No. 2007-212997), it has been performed conventionally to improve system contrast by disposing a plate-type compensator in the neighborhood of the liquid crystal on silicon in an optical system where the field lens is disposed in front of the WG-PBS (lamp side), without disposing the field lens between the liquid crystal on silicon and the WG-PBS. The conventional compensator has a birefringence characteristic which is uniform in a plate plane. On the other hand, in the case of the optical system where the field lens is disposed between the liquid crystal on silicon and the WG-PBS, the non-telecentric light ray enters into the WG-PBS and therefore it is not possible to optimize the contrast over the whole screen region by using the compensator having the birefringence characteristic which is uniform in the plane, and there has been a problem that an in-plane brightness difference is caused in a black output screen.